The present invention relates generally to improvements in thermometers and, more particularly, to electronic thermometers for more rapidly obtaining accurate temperature measurements.
It is common practice in the medical field to determine the body temperature of a patient by means of a temperature sensitive device that not only measures the temperature but also displays that temperature. Such temperature measurements are taken routinely in hospitals and in doctors"" offices. One such device is a glass bulb thermometer incorporating a heat responsive mercury column that expands and contracts adjacent a calibrated temperature scale. Typically, the glass thermometer is inserted into the patient, allowed to remain inserted for a sufficient time interval to enable the temperature of the thermometer to stabilize at the body temperature of the patient, and subsequently removed for reading by medical personnel. This time interval is usually on the order of 3 to 8 minutes.
An electronic thermometer can take one or more minutes in its predictive mode and five or more minutes in its monitoring or direct reading mode. Electronic predictive thermometers have become popular because in their predictive mode, the time for taking the temperature is much less than the mercury thermometer. For busy nursing staffs, time is of the essence. Taking a temperature in one minute is much more desirable than taking a temperature in five minutes. More patients can be served with the faster thermometer and the nursing staff can be more productive.
Additionally, the more time that a probe must be in a patient""s mouth to make a temperature determination, the more likely it is that the probe will not remain in the correct location. This is particularly true with younger patients who tend to be impatient. For patients who cannot be relied upon (by virtue of age or infirmity for example) to properly retain the thermometer for the necessary period of insertion in the body, the physical presence of medical personnel during a relatively long measurement cycle is necessary. Taking a temperature of younger patients in one minute is immensely more desirable than taking the temperature in five minutes. Thus, the predictive electronic thermometer has substantially advanced the art of temperature determination.
In addition to the above, rapid reuse on other patients is also a goal. However, with reuse, precaution must be taken to avoid the possibility of cross contamination between patients. Consequently, protective covers have been designed for use with the probes of thermometers. The protective cover is designed to completely envelope the portion of the thermometer that comes into contact with the patient. Because the protective cover may then be removed after use of the thermometer, and because the protective cover has protected the thermometer from contact with the patient, the thermometer may be immediately reused by simply applying another protective cover.
Protective probe covers have been available for predictive electronic thermometers for many years making the thermometer rapidly reusable when properly used with such covers. However, a protective cover adds material between the temperature sensor in the probe of the thermometer and the heat source; i.e., the patient. Additional material between the patient and the sensor can slow down the process of determining the patient""s temperature as heat from the patient must first pass through the probe cover before it reaches the sensor. Gains made in permitting immediate reuse of thermometers due to the use of a disposable probe cover may thus be offset by the increasing length of time it takes to obtain a reading, caused by that same probe cover.
An inherent characteristic of electronic thermometers is that they do not instantaneously measure the temperature of the site to which they are applied. It may take a substantial period of time before the temperature sensitive device stabilizes at the temperature of the site and the temperature indicated by the thermometer is representative of the actual temperature of the body or site measured. This lag is caused by the various components of the measurement system that impede heat flow from the surface of the body or site to the temperature sensor. Some of the components are the sensor tip, the tissue of the body, and any hygienic probe covering applied to the sensor tip to prevent contamination between measurement subjects.
One approach to shortening the time required for an electronic thermometer to take an accurate reading of a patient""s temperature is to preheat the probe tip of the thermometer to a temperature closer to the expected patient""s temperature. Such probe tip heaters have been known for many years. However, the heater must have enough power to rapidly raise the temperature of the probe cover along with the probe tip. The probe cover adds further considerations, as, depending on the materials of construction, it may have a high heat capacity requiring more power on the part of the heater to raise its temperature. Failure to provide a heater with enough power will result in a slower increase in the temperature of the probe cover.
Applying enough heat to the probe tip to raise its temperature and the temperature of the probe cover to a level closer to the patients"" temperature will reduce the time required for measurement as there is less difference between the temperature of the probe tip and that of the patient. Shortening the time to obtain the patient""s temperature measurement would lessen the risk that the patient would not hold the probe in the correct position for the entire measurement period and requires less time of the attending medical personnel. In addition, the accuracy with which the temperature is predicted improves markedly as the processing and analysis of the data are more accurately performed. This approach has also contributed significantly to the advancement of temperature measurement technology.
A further consideration is the amount of time needed for the probe to preheat. It is undesirable to take the probe out of its well only to have to hold it for a substantial amount of time until it preheats enough to take the patient""s temperature. While there is some advantage in that the probe is not in the patient""s mouth while it is preheating, it still requires time of the medical staff to hold the probe until it is preheated.
While electronic thermometers have advanced the art of thermometry and preheating the probe tips of thermometers is well known, it would be desirable to increase the speed at which the tip may be heated. This would permit faster determination of the patient""s temperature. The invention fulfills these needs and others.
Briefly and in general terms, the present invention is directed to providing a closed loop system and method for heating the probe of a thermometer. In a more detailed aspect, a closed loop heating system is provided that comprises a sensor mounted to the probe, the sensor configured to sense the temperature of the probe and provide a time varying temperature signal in response to the temperature of the probe, a heater mounted at the probe and responsive to heater control signals to provide heat to the probe, a power source, and a processor connected to the power source, the sensor, and the heater so as to provide a closed loop system in heating the probe, the processor providing a drive level of energy from the power source to the heater to cause the heater to heat the probe, the processor applying an offset to the drive level to the heater, the offset being a non-zero value which is a function of ambient temperature and the power source voltage to more rapidly achieve heating of the probe to a target temperature in a stable controlled fashion.
In a further detailed aspect, the processor senses the temperature of the probe and if the temperature of the probe is below a first threshold, the processor is configured to apply a larger level of drive energy to the heater to cause the probe to heat faster, and upon reaching the first threshold, the processor reduces the drive of battery energy to the heater in a proportional manner, the threshold being dependent on the drive level offset.
A method in accordance with aspects of the invention comprises the steps of sensing the temperature of the probe and providing a time varying temperature signal in response to the temperature of the probe, heating the probe in response to heater control signals, and sensing the temperature of the probe and applying heater control signals in a closed loop manner, wherein the heater control signals are applied to the heater at a drive level, and applying an offset to the drive level to the heater, the offset being a non-zero value which is a function of ambient temperature and the power source voltage to more rapidly achieve heating of the probe to a target temperature in a stable controlled fashion.
These and other features and advantages of the present invention will become apparent from the following more detailed description, when taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.